WASHINGTON (AP) — Warm air at high altitudes this September and October helped shrink the man-made ozone hole near the South Pole ever so slightly, scientists say.

The hole is an area in the atmosphere with low ozone concentrations. It is normally is at its biggest this time of year. NASA says on average it covered 8.1 million square miles this season. That's 6 percent smaller than the average since 1990...Butler said it stopped getting worse around the late 1990s. But he added, "We can't say yet that it's a recovery."

This Sunday marks the 25th anniversary of the signing of the world’s most successful environmental treaty, the Montreal Protocol. That’s the treaty that saved the ozone layer, saved millions of lives, and avoided a global catastrophe.